Conditions favoring formation of clathrate hydrates are often found in pipelines. With the expansion of offshore gas exploration and production, the formation of clathrate hydrates has become a serious operational concern in both gas transportation and gas processing. Agglomeration and adherence of clathrate hydrates to pipeline walls can reduce gas production, plug sections of the pipeline, and even block the pipeline, thereby leading to a pipeline shutdown. In order to maintain gas production and avoid pipeline shutdown, clathrate hydrate inhibitors have been added to pipeline fluids.
Commercially available clathrate hydrate inhibitors include thermodynamic hydrate inhibitors (that is, THIs), which act to modify the conditions at which clathrate hydrates form in pipeline fluids. For example, THIs may be added to pipeline fluids at high concentrations (for example, up to 0.8 weight/weight, that is w/w of the water cut) to modify the pressure, temperature, or a combination of the pressure and temperature at which clathrate hydrates form. Ethylene glycol (that is, monoethylene glycol or MEG) and methanol are examples of THIs. Another type of commercially available clathrate hydrate inhibitors are low dose hydrate inhibitors (that is, LDHIs), which act to: (1) kinetically delay clathrate hydrate nucleation, and (2) inhibit clathrate hydrate growth. With regard to kinetically delaying clathrate hydrate nucleation, LDHIs may interact with clathrate hydrate nuclei during early formation of clathrate hydrates. With regard to inhibiting clathrate hydrate growth, LDHIs may inhibit clathrate hydrate growth by binding to a surface of the clathrate hydrate. Poly(N-vinylcaprolactam) and poly(N-methyl-N-vinylacetamide) are examples of LDHIs. A third type of commercially available clathrate hydrate inhibitors are anti-agglomerates (that is, AAs), which act to inhibit clathrate hydrate agglomeration. With regard to inhibiting clathrate hydrate agglomeration, AAs may inhibit clathrate hydrate agglomeration by adsorbing to clathrate hydrates to prevent massive accumulation of clathrate hydrates. In one or more embodiments, AAs may inhibit clathrate hydrate agglomeration such that clathrate hydrates are kept in the form of a suspension. Examples of AAs are anti-agglomerates based on quaternary ammonium cations.
Recently, THIs have been replaced by commercially available LDHIs, because THIs are viewed as being difficult to separate from pipeline fluids, are harmful to the environment, and require high concentrations to be effective. However, commercially available LDHIs are also imperfect in that some are inefficient or incompatible with other additives, for example, corrosion inhibitors. Further, commercially available LDHIs which are capable of inhibiting clathrate hydrates having a structure (Type) I (that is, SI) crystalline structure under severe conditions, for example, extreme subcooling temperatures and pressure, are limited. Moreover, commercially available LDHIs, which are capable of inhibiting clathrate hydrates having a SI crystalline structure, are limited to a narrow subcooling temperature range. Also, AAs are imperfect in that they fail to inhibit formation of clathrate hydrates.